1. Field of the Invention
The present invention relates to an impact absorbing type steering column device designed to protect the driver of a vehicle in the event of a collision.
2. Related Background Art
In the event of a collision of an automobile, a so-called primary collision of the automobile with other vehicles etc. may be followed by a so-called secondary collision of the driver with the steering wheel.
Conventionally, in order to minimize the impact on the driver and thereby reduce the possibility of serious injury, the steering shaft (which holds the steering wheel securely at one end) has been made collapsible, and the steering column through which the steering shaft extends has been provided with an impact absorbing construction.
An example of such an impact absorbing type steering column device is disclosed in Japanese Utility Model Appln. Laid-Open No. 63-76578. This conventional impact absorbing type steering column device has a construction as shown in FIGS. 5-8.
In FIG. 5, 1 indicates a steering shaft, which holds a steering wheel 2 securely at its upper end and which is turned in a torsional direction by operating the steering wheel 2. This steering shaft 1 is constructed with a telescopic mechanism such as a spline joint (not shown) so as to collapse lengthwise when subjected to an axial impact.
3 indicates a tubular steering column, through which the steering shaft 1 extends. The steering column 3 is supported at both its center portion and lower end by a part of a vehicle body 4 such as the lower surface of the dashboard. More particularly the lower end of the steering column 3 is supported by a lower support bracket 5 fixed to a part of the vehicle body 4, so that it can slide axially.
An upper support bracket 6, which has been formed through bending a metal sheet, is fixed to the outer peripheral surface of the center portion of the steering column 3 such as by welding etc. For the attachment of the upper support bracket 6 to the vehicle body 4, a pair of mounting plates 7 are provided on both sides of the upper support bracket 6. Each mounting plate 7 comprises a U-shaped notch 8 opening at one end edge of the plate (the edge disposed toward the steering wheel 2).
9 indicates an elongate-C shaped lock member, which is fitted over the end edge of each mounting plate 7 so as to cover the open end of notch 8. A bolt 10 is inserted through a hole 15 made i the lock member 9 and through the notch 8, and is tightly screwed into a tapped hole provided in the vehicle body 4 so that the mounting plate 7 is clasped tightly by the lock member 9. In this way, the upper support bracket 6 is, via the lock member 9, supported by the vehicle body 4. Alternatively, the bolt 10 may be fixed to the body in advance, and a nut can be screwed on the bolt to secure the lock member 9 and exert a clamping force on the mounting plate 7.
An end portion of an energy absorbing member 11 is connected to each of the mounting plates 7 by welding. The other end of each energy absorbing member 11 comprises a hole 16, through which the corresponding bolt 10 is inserted. The energy absorbing member 11, which is made of a plastically deformable belt-like plate, comprises a U-shaped return 12 in its center portion, and the mounting plate 7 and a guide plate 13 described below clasp this return portion 12 from the upper and lower sides.
On each side of the upper support bracket 6, a respective guide plate 13, which is made through press forming of a metal sheet, is fixed below the mounting plate 7 by welding. A guide space 14 is thus provided between the upper surface of the guide plate 13 and the lower surface of the mounting plate 7 in order to guide the return portion 12 of the energy absorbing member 11.
The function of the above-described impact absorbing type steering column device to protect the driver in the event of a collision is described below.
When an impact is applied on a steering wheel 2 as a result of the secondary collision in an accident, the impact is instantaneously transmitted to the steering column 3, pushing this strongly in the axial direction.
When the impact force, which is applied on the steering column axially, is larger than the frictional force between the mounting plate 7 and the lock member 9 the notch 8 of the mounting plate 7 disengages from the bolt 10, thus releasing the steering column 3.
As a result, the steering column 3 is displaced forwardly in the axial direction (toward the left and downward in FIG. 5), and together with this displacement, the energy absorbing member 11 extends (see FIG. 8) by an amount depending on the impact force. When the energy absorbing member 11 extends from the condition shown in FIG. 5 to the condition in FIG. 8, the return 12 formed in the center portion of the energy absorbing member 11 moves away from the end connected to the bolt 10 (right side in FIG. 8) toward the other end connected to the mounting plate 7 (left side in the same drawing).
During this movement, the return portion of the energy absorbing member 11 undergoes plastic deformation to absorb the impact of the driver's body on the steering column 3 via he steering wheel 2. In addition, in the case of the embodiment in the drawings, a part of the upper surface of the guide plate 13 is tilted so that the guide space 14, where the return portion 12 of the energy absorbing member 11 is guided, may decrease gradually in height. Due to this configuration, the impact force absorbed increases gradually, enabling an effective impact absorption.
Although advantageous in terms of driver safety, the above-described device is problematic from a production point of view, particularly because the number of parts involved complicates parts control and assembly work, thereby increasing the cost. Consider, for example, the need for two energy absorbing members and two guide plates. Because all of these parts are prepared separately from the upper support bracket 6 and must be individually welded to the upper support bracket 6, parts control and assembly work are made more complicated and a high production cost cannot be avoided.
Another type of construction, in which only a single central energy absorbing member is provided, is disclosed in Japanese Utility Model Appln. Laid-Open No. 64-16970. However, it also requires a lot of parts, and accordingly, a high production cost is inevitable.